Waterlogging Stress Memory Including the Tillering Stage Confers the Greatest Tolerance to Waterlogging at Anthesis in Wheat via Enhanced Post-Stress Nitrogen Uptake

Waterlogging stress, particularly during flowering severely constrains wheat production, yet the optimal timing and frequency of waterlogging stress memory and its linkage to post-stress nitrogen acquisition remain unclear. We conducted pot experiments under glasshouse over two consecutive growing seasons (2022/23 and 2023/24) using the Japanese bread wheat cultivar Norin 61 to evaluate eight treatment combinations of waterlogging stress memory applied at the tillering, stem elongation, and booting stages, followed by waterlogging during flowering stage. Leaf greenness (SPAD), chlorophyll fluorescence (Fv′/Fm′), photosynthetic rate, yield and its components, and nitrogen dynamics were assessed. To quantify post-stress nitrogen uptake, 15N-labeled ammonium sulfate was applied immediately after waterlogging termination at flowering, and 15N uptake and allocation to plant organs and grains were determined during grain filling and at harvest. Treatments that included tillering-stage stress memory consistently delayed leaf senescence, maintained higher photosynthetic performance, increased thousand-grain weight, and improved grain yield relative to the non-primed treatment, with reproducible effects across both seasons. These treatments also showed higher post-stress 15N uptake and greater 15N allocation to grains. Overall, tillering-stage waterlogging stress memory was associated with improved tolerance to flowering-stage waterlogging in wheat through maintenance of post-stress nitrogen uptake capacity and nitrogen allocation to grains.